In public speaking there are four kinds of interference.

A．One of the simplest and most important is through a positive feedback loop, where a master transcription regulator activates transcription of its own gene,in addition to that of other cell-typespecific genes. Each time a cell divides, the regulator is distributed to both daughter cells, where it continues to stimulate the positive feedback loop.?The continued stimulation ensures that the regulator will continue to be produced in subsequent cell generations.?Positive feedback is crucial for establishing the “self-sustaining” circuits of gene expression that allow a cell to commit to a particular fate—and then to transmit that decision to its progeny.

B．Although positive feedback loops are probably the most prevalent way of ensuring that daughter cells remember what kind of cells they are meant to be,there are other ways of reinforcing cell identity. One involves the methylation of DNA．In vertebrate cells, DNA methylation occurs on certain cytosine bases. This covalent modification generally turns off the affected genes by attracting proteins that bind to methylated cytosines and block gene transcription. DNA methylation patterns are passed on to progeny cells by the action of an enzyme that copies the methylation pattern on the parent DNA strand to the daughter DNA strand as it is synthesizeD

C．Another mechanism for inheriting gene expression patterns involves the modification of histones. When a cell replicates its DNA,each daughter double helix receives half of its parent’s histone proteins, which contain the covalent modifications that were present on the parent chromosom

E．Enzymes responsible for these modifications may bind to the parental histones and confer the same modifications to the new histones nearby. It has been proposed that this cycle of modification helps reestablish. the pattern of chromatin structure found in the parent chromosome

D．Because all of these cell-memory mechanisms transmit patterns of gene expression from parent to daughter cell without altering the actual nucleotide sequence of the DNA,they are considered to be forms of epigenetic inheritanc

E．These mechanisms, which work together, play an important part in maintaining patterns of gene expression, allowing transient signals from the environment to be remembered by our cells—a fact that has important implications for understanding how cells operate and how they malfunction in diseas

E．

A、E-commerce is the abbreviation for English commerce.

B、E-commerce conducts buying and selling activities only over Internet.

C、The amount of trade conducted electronically has grown extraordinarily with widespread Internet usage.

D、People only sell and buy products instead of services through e-commerce.

A．look

B．see

C．have

D．mind

阅读理解 Starting a restaurant can be rewarding but challenging. Here are some steps to help you to make your restaurant business a success. First, take a look at the restaurants that will be your competition. Learn what your competitors (竞争者) are serving and use the information to create a restaurant that will stand out among them. Speak to people to understand what type of restaurant they would like to have in the area. Next, you will need to make a decision as to what kind of food you plan to offer. Choosing your target customers will help determine what type of food you will offer. Research the different types of menus and select the menu items that will be right for your restaurant. Deciding on the building and its location is also important for your success. Make sure that the building is easily found and reached. It is important to be located in an area that will attract customers. Finally, do plenty of public relations work and advertisement of the restaurant opening. Consider having some special discounts and door prizes on the day of the grand opening. According to the passage, the first step in starting a restaurant is to ____________.

A、find a suitable location.

B、set up your profit goal.

C、learn much about your competitors.

D、advertise the opening of your restaurant.